For many years vehicles have been built wherein the prime mover drives the work function of the vehicle along with propelling the vehicle. Machines of this type would include trenchers, forage harvesters, tillage machines and any other type of machine which moves along as it performs its work function. In the case with most of these machines, and particularly a trencher, the machine does not have enough power to operate its digging mechanism while propelling the machine at its maximum ground speed. Therefore, the operator must listen to the engine, or watch the engine RPM while manually varying the ground speed of the trencher to keep the engine loaded, but at the same time not to overload the engine causing it to stall. This type of manually adjusted system has proven fairly successful, but requires a skilled operator to make constant speed correction to realize anywhere near optimum machine performance. A lesserskilled operator obviously cannot run the machine at anywhere near its peak capacity. Quite often the operator sets the ground speed at some value whereby the engine horsepower used is substantially less than the maximum, and lets the machine operate at this speed, thus not utilizing the full capabilities of the machine.
The present invention provides an automatic system wherein the ground speed of the vehicle is automatically regulated instantaneously so that the full horsepower capacity of the machine is utilized at all times, even though the resistance to digging is constantly changing. The control of the present invention adjusts the ground speed of the machine to keep the engine operating at a substantially constant horsepower at all times. As the digging mechanism encounters softer soil, the machine will increase its ground speed which in turn increases the load or torque on the engine. Likewise, when the digging mechanism engages harder soil it slows down its ground speed just enough to maintain an essentially constant RPM.
It is therefore a principal object of the present invention to provide an automatic horsepower control system which varies the vehicle speed so as to maintain a constant work load torque under varying conditions.
Another object of the present invention is to provide a trencher drive system which varies the vehicle speed in accordance with the digging resistance encountered.
The advantages and objects of the invention will become evident from the following detailed description of the drawings when read in connection with the accompanying drawings which ilustrate a preferred embodiment of the invention.